A number of insecticides are known to affect active and/or passive transport of cations across biological membranes. Recently DDT has been found to inhibit sodium-potassium activated adenosinetriphosphatase (Na- K ATPase). The purpose of the proposed experiments will be to examine the concentration dependence of the effects of selected insecticides on several membrane transport phenomena. Included will be studies on Na, K, and Ca transport and Na-K ATPase activity. The experiments will involve the effects of several insecticides on four different biological systems: the isolated frog skin, intact human erythrocytes, erythrocyte stroma, and isolated intact electroplax cells from the electric eel. The involvement of at least one protein reactive group (sulfhydryl) in any observed effects subsequently will be examined. It is expected that the results will further elucidate the mechanisms by which insecticides alter membrane phenomena and also improve our understanding of the roles of cations and ATPase activity in normal membrane function.